Prostaglandins D2 and E2 have opposite effects on alveolar macrophages infected with Histoplasma capsulatum

Meloxicam treatment disrupts the regional structure of innate inflammation sites by targeting the pro-inflammatory effects of prostanoids

BACKGROUND AND PURPOSE

Non-steroidal anti-inflammatory drugs (NSAIDs) are the most widely prescribed drugs in the world due to their analgesic, antipyretic and anti-inflammatory effects. However, NSAIDs inhibit prostanoid synthesis, interfering with their pro-inflammatory and anti-inflammatory functions and potentially prolonging acute inflammation.

EXPERIMENTAL APPROACH

We used high-content immunohistochemistry to define the impact of meloxicam treatment on spatially separated pro-inflammatory and anti-inflammatory processes during innate inflammation in mice induced by zymosan. This allowed us to determine the effect of meloxicam treatment on the organization of pro-inflammatory and anti-inflammatory microenvironments, thereby identifying relevant changes in immune cell localization, recruitment and activation.

KEY RESULTS

Meloxicam treatment reduced zymosan-induced thermal hypersensitivity at early time points but delayed its resolution. High-content immunohistochemistry revealed that the pro-inflammatory area was smaller after treatment, diminishing neutrophil recruitment, M1-like macrophage polarization, and especially phagocytosis by neutrophils and macrophages. The polarization of macrophages towards the M2-like anti-inflammatory phenotype was unaffected, and the number of anti-inflammatory eosinophils actually increased.

CONCLUSION AND IMPLICATIONS

High-content immunohistochemistry was able to identify relevant meloxicam-mediated effects on inflammatory processes based on alterations in the regional structure of inflammation sites. Meloxicam delayed the clearance of pathogens by inhibiting pro-inflammatory processes, causing prolonged inflammation. Our data suggest that the prescription of NSAIDs as a treatment during an acute pathogen-driven inflammation should be reconsidered in patients with compromised immune systems.

An integrative multi-omics approach to characterize interactions between tuberculosis and diabetes mellitus

Tuberculosis-diabetes mellitus (TB-DM) is linked to a distinct inflammatory profile, which can be assessed using multi-omics analyses. Here, a machine learning algorithm was applied to multi-platform data, including cytokines and gene expression in peripheral blood and eicosanoids in urine, in a Brazilian multi-center TB cohort. There were four clinical groups: TB-DM(n = 24), TB only(n = 28), DM(HbA1c ≥ 6.5%) only(n = 11), and a control group of close TB contacts who did not have TB or DM(n = 13). After cross-validation, baseline expression or abundance of MMP-28, LTE-4, 11-dTxB2, PGDM, FBXO6, SECTM1, and LINCO2009 differentiated the four patient groups. A distinct multi-omic-derived, dimensionally reduced, signature was associated with TB, regardless of glycemic status. SECTM1 and FBXO6 mRNA levels were positively correlated with sputum acid-fast bacilli grade in TB-DM. Values of the biomarkers decreased during the course of anti-TB therapy. Our study identified several markers associated with the pathophysiology of TB-DM that could be evaluated in future mechanistic investigations.

Lipid droplets in pathogen infection and host immunity

As the hub of cellular lipid metabolism, lipid droplets (LDs) have been linked to a variety of biological processes. During pathogen infection, the biogenesis, composition, and functions of LDs are tightly regulated. The accumulation of LDs has been described as a hallmark of pathogen infection and is thought to be driven by pathogens for their own benefit. Recent studies have revealed that LDs and their subsequent lipid mediators contribute to effective immunological responses to pathogen infection by promoting host stress tolerance and reducing toxicity. In this comprehensive review, we delve into the intricate roles of LDs in governing the replication and assembly of a wide spectrum of pathogens within host cells. We also discuss the regulatory function of LDs in host immunity and highlight the potential for targeting LDs for the diagnosis and treatment of infectious diseases.

Polyunsaturated Fatty Acid-Derived Lipid Mediators as Potential Biomarkers for Leprosy Among Individuals with Asymptomatic Mycobacterium leprae Infection

Intra-household contacts (HCs) of leprosy patients are at increased risk of infection by Mycobacterium leprae and about ∼5-10% will develop active disease. A prognostic tool to identify HCs with the greatest risk of progressing to active disease would enhance early leprosy diagnosis and optimize prophylactic intervention. Previous metabolomics studies suggest that host lipid mediators derived from ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) are potential biomarkers for leprosy. In this study, we investigated retrospective sera of leprosy HCs by liquid chromatography-mass spectrometry and enzyme-linked immunoassay to determine whether circulating levels of ω-3 and ω-6 PUFA metabolites were altered in HCs that developed leprosy (HCDL) in comparison to those that did not (HCNDL). Sera were collected from HCs at the time of index case diagnosis and before clinical signs/symptoms of leprosy. Our findings showed that HCDL sera exhibited a distinct metabolic profile in comparison to HCDNL. Specifically, arachidonic acid, leukotriene B4, 11-hydroxyeicosatetraenoic acid, prostaglandin D2, and lipoxin A4 were elevated in HCDL. In contrast, prostaglandin E2 levels were reduced in HCDL. The ω-3 PUFAs, docosahexaenoic acid, eicosapentaenoic acid, and the docosahexaenoic acid-derived resolvin D1 and maresin-1 were also elevated in HCDL individuals compared to HCNDL. Principal component analyses provided further evidence that lipid mediators could serve as an early biomarker for progression to active leprosy. A logistic model identified resolvin D1 and D2, and prostaglandin D2 as having the greatest potential for early detection of HCs that will manifest leprosy.

Leukotriene B4 Loaded in Microspheres Inhibits Osteoclast Differentiation and Activation

To investigate osteoclast formation in vivo and if leukotriene B4 (LTB4) loaded in microspheres (MS) could be used as a therapeutical strategy to promote a sustained delivery of the mediator and prevent osteoclast differentiation. Methods: In vivo, apical periodontitis was induced in mice to investigate osteoclast differentiation and signaling in absence of 5-lipoxygenase (5-LO). In vitro, LTB4-MS were prepared using an oil-in-water emulsion solvent extraction-evaporation process. Characterization and efficiency of LTB4 encapsulation were investigated. J774A.1 macrophages were cultured in the presence of monocyte colony-stimulating factor (M-CSF) and ligand for receptor activator of nuclear factor kappa B (RANKL) and then stimulated with LTB4-MS. Cytotoxicity, in vitro MS-LTB4 uptake, osteoclast formation and gene expression were measured. Results: We found that 5-LO negatively regulates osteoclastic formation in vivo during apical periodontitis development. In vitro, LTB4-MS were up-taken by macrophages and were not cytotoxic to the cells. LTB4-MS inhibited osteoclast formation and the synthesis of osteoclastogenic genes Acp5, Mmp9, Calcr and Ctsk. LTB4-MS inhibited differentiation of macrophages into an osteoclastic phenotype and cell activation under M-CSF and RANKL stimulus.

A new polysaccharide from Caulerpa chemnitzia induces molecular shifts of immunomodulation on macrophages RAW264.7

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CCP showed significant immunomodulatory effects.

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CCP raising the level of NO, TNF-α, and IL-6 of macrophages RAW264.7.

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Investigation on the metabolites and genes changes in CCP-induced RAW264.7.

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Potential immunostimulatory mechanism of CCP on RAW264.7 was elucidated.

Investigation on Caulerpa chemnitzia polysaccharides led to the finding of a new polysaccharide (CCP). The basic components of CCP were the total sugar (59.18% ± 0.57%), the uronic acids (36.75% ± 0.28%) and the sulfate (42.50% ± 0.42%), in total content. The physicochemical analysis revealed that CCP was a heteropolysaccharide with a molecular weight of 321.6 KDa, and composed of arabinose, fucose, glucose, mannose, galactose, xylose, fructose, ribose, glucuronic acid and galacturonic acid. The immunomodulatory assay showed that CCP played an important role in activating cell viability, the nitric oxide product and cytokines (IL-6 and TNF-α) secretion. Furthermore, the transcript-metabolic analysis displayed a total of 7692 differentially expressed genes (DEGs) and 95 differentially accumulated metabolites (DAMs), and revealed that CCP may play an immunomodulatory effect by activating NF-κB signaling pathway and arachidonic acid metabolism pathway. These findings will provide a basic understanding to further investigation of Caulerpa polysaccharides.

Celecoxib treatment dampens LPS-induced periapical bone resorption in a mouse model

AIM

To evaluate the efficacy of selective and nonselective inhibitors of cyclooxygenase-2 enzymes in the treatment of experimental apical periodontitis induced by bacterial lipopolysaccharide (LPS) in vivo in a mouse model.

METHODOLOGY

Thirty-six C57BL/6 mice were used. After access cavity preparation, a solution containing E. coli LPS (1.0 µg µL^-1 ) was inoculated into the root canals of the mandibular and maxillary right first molars (n = 72) After 30 days, apical periodontitis was established and the animals were systemically treated with celecoxib, a selective COX-2 inhibitor (15 mg kg^-1 ), or indomethacin, a nonselective COX-2 inhibitor (5 mg kg^-1 ), for 7 and 14 days. Blocks containing teeth and bone were removed for histopathological and histometric analyses (haematoxylin and eosin), evaluation of osteoclasts numbers (tartrate-resistant acid phosphatase enzyme - TRAP) and immunohistochemistry for RANK, RANKL and OPG. Gene expression was performed using reverse transcription and real-time polymerase chain reaction (qRT-PCR) for RANK, RANKL, OPG, TRAP, MMP-9, cathepsin K and calcitonin receptor. Histopathological, histometric, TRAP, immunohistochemistry and qRT-PCR data were evaluated using Kruskal-Wallis followed by Dunn's test (α = 0.05).

RESULTS

Systemic administration of celecoxib for 7 and 14 days prevented periapical bone resorption (P < 0.0001), differently from indomethacin that exacerbated bone resorption at 7 days (P < 0.0001) or exerted no effect at 14 days (P = 0.8488). Celecoxib treatment reduced osteoclast formation in apical periodontitis, regardless of the period of treatment (P < 0.0001 for 7 days and P = 0.026 for 14 days). Administration of celecoxib or indomethacin differentially modulated the expression of genes involved in bone resorption. At 7 days, celecoxib and indomethacin treatment significantly inhibited expression of mRNA for cathepsin K (P = 0.0005 and P = 0.016, respectively) without changing TRAP, MMP-9 and calcitonin receptor gene expression. At 14 days, celecoxib significantly inhibited expression of mRNA for MMP-9 (P < 0.0001) and calcitonin receptor (P = 0.004), whilst indomethacin exerted no effect on MMP-9 (P = 0.216) and calcitonin receptor (P = 0.971) but significantly augmented cathepsin K gene expression (P = 0.001).

CONCLUSIONS

The selective COX-2 inhibitor celecoxib reduced osteoclastogenic signalling and activity that dampened bone resorption in LPS-induced apical periodontitis in mice, with greater efficacy than the nonselective inhibitor indomethacin.

Complex and Controversial Roles of Eicosanoids in Fungal Pathogenesis

The prevalence of fungal infections has increased in immunocompromised patients, leading to millions of deaths annually. Arachidonic acid (AA) metabolites, such as eicosanoids, play important roles in regulating innate and adaptative immune function, particularly since they can function as virulence factors enhancing fungal colonization and are produced by mammalian and lower eukaryotes, such as yeasts and other fungi (Candida albicans, Histoplasma capsulatum and Cryptococcus neoformans). C. albicans produces prostaglandins (PG), Leukotrienes (LT) and Resolvins (Rvs), whereas the first two have been well documented in Cryptococcus sp. and H. capsulatum. In this review, we cover the eicosanoids produced by the host and fungi during fungal infections. These fungal-derived PGs have immunomodulatory functions analogous to their mammalian counterparts. Prostaglandin E₂ (PGE₂) protects C. albicans and C. parapsilosis cells from the phagocytic and killing activity of macrophages. H. capsulatum PGs augment the fungal burden and host mortality rates in histoplasmosis. However, PGD₂ potentiates the effects and production of LTB₄, which is a very potent neutrophil chemoattractant that enhances host responses. Altogether, these data suggest that eicosanoids, mainly PGE₂, may serve as a new potential target to combat diverse fungal infections.

Lipid metabolism in asthma: Immune regulation and potential therapeutic target

Asthma is a chronic inflammatory disease of the lungs that poses a considerable health and socioeconomic burden. Several risk factors work synergistically to affect the progression of asthma. Lipid metabolism, especially in distinct cells such as T cells, macrophages, granulocytes, and non-immune cells, plays an essential role in the pathogenesis of asthma, as lipids are potent signaling molecules that regulate a multitude of cellular response. In this review, we focused on the metabolic pathways of lipid molecules, especially fatty acids and their derivatives, and summarized their roles in various cells during the pathogenesis of asthma along with the current pharmacological agents targeting lipid metabolism.

Eosinophils increase macrophage ability to control intracellular Leishmania amazonensis infection via PGD2 paracrine activity in vitro

Clinical and experimental studies have described eosinophil infiltration in Leishmania amazonensis infection sites, positioning eosinophils strategically adjacent to the protozoan-infected macrophages in cutaneous leishmaniasis. Here, by co-culturing mouse eosinophils with L. amazonensis-infected macrophages, we studied the impact of eosinophils on macrophage ability to regulate intracellular L. amazonensis infection. Eosinophils prevented the increase in amastigote numbers within macrophages by a mechanism dependent on a paracrine activity mediated by eosinophil-derived prostaglandin (PG) D₂ acting on DP2 receptors. Exogenous PGD₂ mimicked eosinophil-mediated effect on managing L. amazonensis intracellular infection by macrophages and therefore may function as a complementary tool for therapeutic intervention in L. amazonensis-driven cutaneous leishmaniasis.

COVID-19: Integrating the Complexity of Systemic and Pulmonary Immunopathology to Identify Biomarkers for Different Outcomes

In the last few months, the coronavirus disease 2019 (COVID-19) pandemic has affected millions of people worldwide and has provoked an exceptional effort from the scientific community to understand the disease. Clinical evidence suggests that severe COVID-19 is associated with both dysregulation of damage tolerance caused by pulmonary immunopathology and high viral load. In this review article, we describe and discuss clinical studies that show advances in the understanding of mild and severe illness and we highlight major points that are critical for improving the comprehension of different clinical outcomes. The understanding of pulmonary immunopathology will contribute to the identification of biomarkers in an attempt to classify mild, moderate, severe and critical COVID-19 illness. The interface of pulmonary immunopathology and the identification of biomarkers are critical for the development of new therapeutic strategies aimed to reduce the systemic and pulmonary hyperinflammation in severe COVID-19.

Interleukin-1 receptor-induced PGE2 production controls acetylcholine-mediated cardiac dysfunction and mortality during scorpion envenomation

Scorpion envenomation is a leading cause of morbidity and mortality among accidents caused by venomous animals. Major clinical manifestations that precede death after scorpion envenomation include heart failure and pulmonary edema. Here, we demonstrate that cardiac dysfunction and fatal outcomes caused by lethal scorpion envenomation in mice are mediated by a neuro-immune interaction linking IL-1 receptor signaling, prostaglandin E_2, and acetylcholine release. IL-1R deficiency, the treatment with a high dose of dexamethasone or blockage of parasympathetic signaling using atropine or vagotomy, abolished heart failure and mortality of envenomed mice. Therefore, we propose the use of dexamethasone administration very early after envenomation, even before antiserum, to inhibit the production of inflammatory mediators and acetylcholine release, and to reduce the risk of death.

Cardiac dysfunction is a major complication that precedes death after scorpion envenomation. Here, authors show that heart failure and mortality are caused by excessive acetylcholine release, which requires IL-1R-dependent PGE2 production. Dexamethasone treatment effectively inhibits cardiac dysfunction and mortality.

Lipid Players of Cellular Senescence

Lipids are emerging as key players of senescence. Here, we review the exciting new findings on the diverse roles of lipids in cellular senescence, most of which are enabled by the advancements in omics approaches. Senescence is a cellular process in which the cell undergoes growth arrest while retaining metabolic activity. At the organismal level, senescence contributes to organismal aging and has been linked to numerous diseases. Current research has documented that senescent cells exhibit global alterations in lipid composition, leading to extensive morphological changes through membrane remodeling. Moreover, senescent cells adopt a secretory phenotype, releasing various components to their environment that can affect the surrounding tissue and induce an inflammatory response. All of these changes are membrane and, thus, lipid related. Our work, and that of others, has revealed that fatty acids, sphingolipids, and glycerolipids are involved in the initiation and maintenance of senescence and its associated inflammatory components. These studies opened up an exciting frontier to investigate the deeper mechanistic understanding of the regulation and function of these lipids in senescence. In this review, we will provide a comprehensive snapshot of the current state of the field and share our enthusiasm for the prospect of potential lipid-related protein targets for small-molecule therapy in pathologies involving senescence and its related inflammatory phenotypes.

IL-22 Promotes IFN-γ-Mediated Immunity against Histoplasma capsulatum Infection

Histoplasma capsulatum is the agent of histoplasmosis, one of the most frequent mycoses in the world. The infection initiates with fungal spore inhalation, transformation into yeasts in the lungs and establishment of a granulomatous disease, which is characterized by a Th1 response. The production of Th1 signature cytokines, such as IFN-γ, is crucial for yeast clearance from the lungs, and to prevent dissemination. Recently, it was demonstrated that IL-17, a Th17 signature cytokine, is also important for fungal control, particularly in the absence of Th1 response. IL-22 is another cytokine with multiple functions on host response and disease progression. However, little is known about the role of IL-22 during histoplasmosis. In this study, we demonstrated that absence of IL-22 affected the clearance of yeasts from the lungs and increased the spreading to the spleen. In addition, IL-22 deficient mice (Il22-/-) succumbed to infection, which correlated with reductions in the numbers of CD4+ IFN-γ+ T cells, reduced IFN-γ levels, and diminished nitric oxide synthase type 2 (NOS2) expression in the lungs. Importantly, treatment with rIFN-γ mitigated the susceptibility of Il22-/- mice to H. capsulatum infection. These data indicate that IL-22 is crucial for IFN-γ/NO production and resistance to experimental histoplasmosis.

Pulmonary surfactant phosphatidylcholines induce immunological adaptation of alveolar macrophages

Pulmonary surfactant plays an important role in lung surface tension, defense against invading pathogens, and immune response. Furthermore, alveolar macrophages (AM) that comprise the front line of immune defense against inhaled microorganisms are covered by a layer of pulmonary fluid. Phosphatidylcholines (PCs), including unsaturated lipids such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), are the most prevalent phospholipids in pulmonary surfactant. POPC reacts with ozone to produce 1-palmitoyl-2-(9-oxo-nonanoyl)-sn-glycero-3-phosphocholine (PONPC), a soluble mediator that initiates an inflammatory reaction in the lungs. However, the modulatory effects of POPC and PONPC on biology and activity of AM remain inconclusive. The exposure of AM (cell line AMJ2-C11) to POPC and PONPC was not directly related to the production of inflammatory mediators. However, AM, pre-incubated with POPC or PONPC, showed enhanced response after lipopolysaccharide (LPS) stimulation, and increased the production of nitric oxide and cytokines. This phenomenon was also observed for classical-polarized macrophages (M1). This increment on the production of inflammatory mediators was not associated with macrophage polarization, but with up-regulation of Tlr4 and Myd88 gene expression, which was in accordance with the adaptation of immune cells. This observation was confirmed by the histone acetylation epigenetic pathway. In contrast to the priming effect of POPC on AM activity, a harmful immune response, induced on incubation with PONPC, improved prostaglandin E2 (PGE2) formation, resulting in diminished bacterial phagocytosis. Additionally, PONPC induced production of CXCL1/KC, which potentially mediates neutrophil recruitment and enhances tissue inflammation. These results disclosed another dynamic mechanism by which pulmonary surfactant lipids (natural or oxidized) primed macrophage activity, thus affecting lung host defense.

Prostaglandin E2 Induces Expression of Mineralization Genes by Undifferentiated Dental Pulp Cells

Abstract Prostaglandin E2 (PGE2) is a lipid mediator usually released during inflammation. This study aimed to investigate the potential of soluble or microsphere-loaded PGE2 on inducing differentiation of dental pulp stem cells. PGE2-loaded microspheres (MS) were prepared using an oil-in-water emulsion solvent extraction-evaporation process and were characterized. Mouse dental pulp stem cells (OD-21) were stimulated with soluble or PGE2-loaded MS (0.01 and 0.1 µM). Cell viability was determined by MTT colorimetric assay. Ibsp, Bmp2 and Runx2 expression was measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR) after 3, 6, and 24 h. The results showed that the soluble PGE2 reduced dental pulp stem cells viability after 24 h of stimulation whereas PGE2-loaded MS did not. Soluble PGE2 up-regulated Ibsp and Bmp2 at 3 h, differently from PGE2-loaded MS. On the other hand, PGE2-MS induced Bmp2 and Runx2 at 6 h and Ibsp at 24 h. In conclusion, our in vitro results show that PGE2, soluble or loaded in MS are not cytotoxic and modulateIbsp,Bmp2, andRunx2gene expression in cultured OD-21 cells.

Prostaglandin E2 Inhibits the Ability of Neutrophils to Kill Listeria monocytogenes

PGE₂ is a lipid-signaling molecule with complex roles in both homeostasis and inflammation. Depending on the cellular context, PGE₂ may also suppress certain immune responses. In this study, we tested whether PGE₂ could inhibit bacterial killing by polymorphonuclear neutrophils (PMN) using a mouse model of foodborne listeriosis. We found that PGE₂ pretreatment decreased the ability of PMN harvested from the bone marrow of either BALB/cByJ or C57BL/6J mice to kill Listeria monocytogenes in vitro. PGE₂ treatment slowed the migration of PMN toward the chemoattractant leukotriene B4, decreased uptake of L. monocytogenes by PMN, and inhibited the respiratory burst of PMN compared with vehicle-treated cells. When immune cells were isolated from the livers of infected mice and tested directly ex vivo for the presence of PGE₂, BALB/cByJ cells produced significantly more than C57BL/6J cells. Together, these data suggest that robust PGE₂ production can suppress PMN effector functions, leading to decreased bacterial killing, which may contribute to the innate susceptibility of BALB/cByJ mice to infection with the facultative intracellular bacterial pathogen L. monocytogenes.

Lipid metabolism in inflammation-related diseases

There are thousands of lipid species existing in cells, which belong to eight different categories. Lipids are the essential building blocks of cells. Recent studies have started to unveil the important functions of lipids in regulating cell metabolism. However, we are still at a very early stage in fully understanding the physiological and pathological functions of lipids. The application of lipidomics for studying lipid metabolism can provide a direct readout of the cellular status and broadens our understanding of the mechanisms that underpin metabolic disease states. This review provides an introduction to lipid metabolism and its role in modulating homeostasis and immunity. We also describe representative applications of lipidomics for studying lipid metabolism in inflammation-related diseases.

EP80317 Restrains Inflammation and Mortality Caused by Scorpion Envenomation in Mice

Over 1 million cases of scorpion stings are estimated every year, whereas current treatment is limited to antivenom serum combined with supportive therapy. Tityus serrulatus scorpion venom (TsV) is composed of diverse molecules, including toxins that induce a catecholamine storm and mediate classical symptoms of scorpion envenomation. However, the same toxins promote an intense inflammatory response coordinated by innate immune cells, such as macrophages, contributing significantly to the lung edema and mortality caused by TsV injection. Macrophages sense TsV via innate immune receptors, including TLR2, TLR4, and CD14 that promote inflammation and mortality via PGE₂/cAMP/PKA/NF-κB/IL-1β axis. The scavenger receptor CD36 also recognizes TsV, but in contrast to the other receptors, it drives the production of leukotriene B₄ (LTB₄). This lipid mediator operates via BLT1 receptor to reduce cAMP production and consequently IL-1β release, which results in resistance to fatal outcomes of experimental scorpion envenomation. EP80317 is an hexapeptide that serves as a ligand for CD36 and features protective effects under conditions such as atherosclerosis and vascular inflammation. In this study, we evaluated the effects of EP80317 treatment during experimental scorpion envenomation. EP80317 treatment suppressed mouse peritoneal macrophage production of IL-1β, IL-6, tumor necrosis factor (TNF-α), CCL3, and PGE₂ in vitro. EP80317 treatment also boosted the production of LTB₄ and IL-10 in response to TsV. Importantly, EP80317 restrained lung inflammation and mortality caused by TsV in vivo. Taken together, these data indicate a strong therapeutic potential of EP80317 as a supportive treatment to control inflammation induced by scorpion envenomation.

Augmented liver inflammation in a microsomal prostaglandin E synthase 1 (mPGES-1)-deficient diet-induced mouse NASH model

In a subset of patients, non-alcoholic fatty liver disease (NAFLD) is complicated by cell death and inflammation resulting in non-alcoholic steatohepatitis (NASH), which may progress to fibrosis and subsequent organ failure. Apart from cytokines, prostaglandins, in particular prostaglandin E₂ (PGE₂), play a pivotal role during inflammatory processes. Expression of the key enzymes of PGE₂ synthesis, cyclooxygenase 2 and microsomal PGE synthase 1 (mPGES-1), was increased in human NASH livers in comparison to controls and correlated with the NASH activity score. Both enzymes were also induced in NASH-diet-fed wild-type mice, resulting in an increase in hepatic PGE₂ concentration that was completely abrogated in mPGES-1-deficient mice. PGE₂ is known to inhibit TNF-α synthesis in macrophages. A strong infiltration of monocyte-derived macrophages was observed in NASH-diet-fed mice, which was accompanied with an increase in hepatic TNF-α expression. Due to the impaired PGE₂ production, TNF-α expression increased much more in livers of mPGES-1-deficient mice or in the peritoneal macrophages of these mice. The increased levels of TNF-α resulted in an enhanced IL-1β production, primarily in hepatocytes, and augmented hepatocyte apoptosis. In conclusion, attenuation of PGE₂ production by mPGES-1 ablation enhanced the TNF-α-triggered inflammatory response and hepatocyte apoptosis in diet-induced NASH.